This invention relates to the field of television receivers and, more particularly, to receivers for receiving both 525-line interlaced pictures and 787.5-line progressively scanned pictures.
At the present time, there are millions of television receivers in use throughout the world. In the United States and a number of other countries these receivers are designed to use a set of television standards established in 1939 for black and white pictures by the National Television Systems Committee (NTSC) under the auspices of the Federal Communications Commission (FCC), and modified in 1953 to include color displays. However, there is an active interest in obtaining pictures with higher resolution than is possible within the NTSC standards. A number of systems have been proposed or are being developed which provide some measure of higher resolution, but many of these systems are not compatible with present receivers. One answer to the requirement for compatibility is some means for providing dual function in a receiver; i.e., the capability of receiving both NTSC and HDTV signals. In presently known systems for providing both capabilities in a single receiver, a relatively complicated process is required for converting the interlaced scan of the NTSC system to a progressive scan since it is necessary to store an entire frame at a time and "re-scan" the frame in order to perform the conversion. This large amount of storage and associated logic adds an undesirable expense in the receiver. It is a desirable goal to provide a dual function receiver without such an expensive process.